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Re: [XPath] is it legal ?

• To: Philippe Poulard <Philippe.Poulard@s...>
• Subject: Re: [XPath] is it legal ?
• From: Jeff Rafter <lists@j...>
• Date: Fri, 07 Apr 2006 10:04:55 -0700
• Cc: Michael Kay <mike@s...>, xml-dev@l...
• In-reply-to: <44368069.1080603@s...>
• References: <200604071216.k37CGoqd030079@s...> <44368069.1080603@s...>
• Reply-to: lists@j...
• User-agent: Thunderbird 1.5 (Windows/20051201)

<snip/>

> It appears that what is needed, is :
> -also 4 kind of sizes
> -a mean to read forward SAX events
> To achieve this, I intend to write a cache that could store some events 
> (limited to 100 or 1000 or whatever you set as a default parameter) ; 
> thus, when a size is requested, the engine goes on reading the input 
> until the information is known, then the step is evaluated and later, 
> the events stored will be fetched.
> This is a smart strategy because it is not limited to count(), but to 
> any operations that expect more reading, thus a predicate that contains 
> following-sibling:: may also be considered. The idea is to use the cache 
> only when it is explicitely expected (putting all a document in a cache 
> wouldn't be SAX, but DOM). The events could also be cached in a tree 
> fragment, I don't know yet what is the best way to achieve this.
> 
> Of course there are examples when the information expected is not 
> reachable in the limit of the cache size, or lost because it has been 
> previously read, but it will help in many other examples.
> As I have some code that allows to pour SAX events into DOM trees, I'll 
> provide a smart mean to match a pattern on the SAX entry, and process 
> the subtree with full XPath capabilities ; this might be very helpfull 
> for very large documents.
> 
> What do you think of such a strategy ?
> Did you made something similar in Saxon ?

<snip/>


You might want to take a look at XML Path Event API (XPEA) [1] by Karl 
Waclawek. Also, there is some work in .NET about caching based XmlReader 
implementations (I think Oleg or Dare had a blog post on this). In 
general decoupling the caching allowed for a fair amount flexibility 
down the road.

Cheers,
Jeff Rafter

[1]http://sourceforge.net/projects/xpea

• References:
  • Re: [XPath] is it legal ?
    • From: Philippe Poulard <Philippe.Poulard@s...>

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